This patent application claims priority under 35 U.S.C. xc2xa7 119 from Italian Patent Application No. M197 A 002362, filed Oct. 20, 1997, which is incorporated herein by reference for all purposes.
The present invention relates generally to plasma flat panel displays and, more particularly, to a getter system for plasma flat panel displays.
Plasma flat panel displays, which are sometimes referred to as xe2x80x9cplasma display panelsxe2x80x9d or xe2x80x9cPDP,xe2x80x9d have long been studied as potential replacements for the cathode ray tube (CRT) displays presently used in devices such as televisions and computer monitors. It is expected that commercial products incorporating plasma flat panel displays will be brought to market in the near future.
A plasma flat panel display includes front and rear glass panels that are sealingly joined together along their peripheral edges with a low-melting point glass paste. A number of functional components, e.g., electrodes and phosphors, are provided in the inner space between the front and rear glass panels, which is filled with a mixture of rare gases. The principle of operation of a plasma flat panel display is the conversion of ultraviolet radiation into visible light by phosphors. The ultraviolet radiation is generated in the rare gas mixture when an electrical discharge is produced therein. Thus, to use a plasma flat panel display as a screen for a television or a computer monitor, it is apparent that a plurality of extremely small light sources is needed to form a suitable image. To satisfy this requirement, a plurality of electrode pairs for generating localized electrical discharges is provided in the inner space between the front and rear glass panels. The electrical discharges generated by the electrode pairs are confined within a small area by not only applying a potential difference to a predetermined pair of single electrodes, but also dividing the inner space between the front and rear glass panels into a series of microspaces, e.g., parallel channels having a width of about 0.1-0.3 mm.
FIGS. 1 and 2 illustrate the configurations used to define microspaces in two known plasma flat panel displays. As shown in FIG. 1, plasma flat panel display 10 includes front glass panel 11 and rear glass panel 12. Front glass panel 11 carries a first series of electrodes 13 (indicated by the dashed lines) and rear glass panel 12 carries a second series of electrodes 14. Walls 15 define a plurality of parallel channels 16, each of which has one of electrodes 14 located therein. The second series of electrodes 14 is orthogonal to the first series of electrodes 13. Referring to FIG. 2, in plasma flat panel display 20 a plurality of cell structures 21 divide the space between front glass panel 11 and rear glass panel 12 into small cells having a side dimension of, e.g., 0.1-0.3 mm. The cell structures 21 also define a plurality of parallel channels 16. As shown in FIG. 2, the second series of electrodes 14 is oriented so that the electrodes pass through channels 16, i.e., the electrodes are perpendicular to the direction of channels 16. In plasma flat panel display 20 the first series of electrodes 13, which is not shown in FIG. 2, is orthogonal to the second series of electrodes 14.
The structures that define the microspaces, e.g., simple walls as shown in FIG. 1 or more complex cell structures as shown in FIG. 2, extend over the entire surface of the front and rear glass panels, except for an edge area at the perimeter of the panels. In operation an image is formed on the front glass panel in an image-forming area, which corresponds with the area over which the microspace-defining structures extend. The edge area, which is typically 2-15 mm wide depending on the dimensions of the plasma flat panel display, defines a channel that has a high gas conductance and therefore serves as the primary gas conductance within the inner space between the front and rear glass panels. The channels defined in the image-forming area have a much lower gas conductance than the channel in the edge area and therefore serve as secondary gas conductance sources.
The rare gas mixture used to fill the inner space between the front and rear gas panels generally consists of helium and neon with minor amounts of xenon or argon. To ensure proper operation of a plasma flat panel display, the chemical composition of the rare gas mixture in which the plasma is formed must remain constant. If traces of atmospheric gases such as nitrogen, oxygen, water, or carbon oxides enter the rare gas mixture, then changes in the electrical operating parameters of the plasma flat panel display occur, as disclosed in the publication by W. E. Ahearn and O. Sahni, xe2x80x9cEffect of reactive gas dopants on the MgO surface in AC plasma display panels,xe2x80x9d IBM J. Res. Dev., Vol. 22, No. 6, November 1978, pp. 622-625. In the manufacturing of plasma flat panel displays, after the front and rear glass panels have been joined together, atmospheric gases are evacuated from the inner space by means of a pump connected to the inner space by means of a tiny hole formed at a corner of one of the panels at a position corresponding to the edge area. The rate at which the atmospheric gases can be evacuated from the inner space is limited because all the gas in the channels defined in the image-forming area flows into the channel at the edge area, thus creating an accumulation of gas that cannot be quickly removed. The pressure variation in the various areas of the inner space has not been studied in depth and, consequently, plasma flat panel display manufacturers use empirically determined evacuation times of several hours as a compromise between the conflicting demands of minimizing production time (and costs) and obtaining low residual pressures of atmospheric gases required for proper operation of the display. Another source of impurities in the inner space is the degassing of the materials disposed therein, e.g., the phosphors, caused by the heating and electronic bombardment that occurs during operation of the display.
Japanese Patent Publication No. 5-342991 discloses method of removing impurities from the inner space during the manufacturing of a plasma flat panel display. In this method a deposit of porous magnesium oxide, MgO, is provided along an edge of the display, with the ends of the deposit being connected to a source of direct current. When a voltage is applied, the MgO deposit is capable of sorbing certain impurities, e.g., water and carbon dioxide, from the inner space. Once the manufacturing process is finished, however, the electrical contacts are removed and the MgO deposit loses its ability to sorb impurities. Consequently, the MgO deposit does not sorb the gaseous impurities generated by the degassing of the components disposed within the inner space. Thus, this method does not provide a solution to the degassing problem, which causes the gaseous impurity concentration within the inner space to increase over the course of the display""s service life.
In view of the foregoing, there is a need for an improved process of evacuating the inner space of plasma flat panel displays during manufacturing that reduces evacuation time. There is also a need for a mechanism for sorbing gaseous impurities that are generated within the inner space during the display""s service life.
Broadly speaking, the invention fills this need by providing a getter system for use in plasma flat panel displays. The getter system includes one or more nonevaporable getter devices that are configured so that they do not significantly reduce the gas conductance within the inner space defined by the front and rear panels of the display.
In one aspect of the invention, a getter system for use in a plasma flat panel display is provided. The plasma flat panel display preferably has front and rear panels sealingly joined together at peripheral edges thereof to define an inner space and a plurality of walls disposed within the inner space. These walls define a series of substantially parallel secondary channels with openings at first and second ends thereof and a main channel extending along the perimeter of the front and rear panels. The getter system includes at least one nonevaporable getter device disposed within the inner space. The at least one nonevaporable getter device is preferably located in a portion of the main channel that faces the openings at one of the first and second ends of the secondary channels.
In one embodiment the getter system includes first and second nonevaporable getter devices disposed within the inner space. The first nonevaporable getter device is located in a portion of the main channel that faces the openings at the first end of the secondary channels and the second nonevaporable getter device is located in a portion of the main channel that faces the openings at the second end of the secondary channels.
In one embodiment the at least one nonevaporable getter device is a deposit comprised of powdered nonevaporable getter material. The deposit preferably continuously covers the portion of the main channel that faces the openings at one of the first and second ends of the secondary channels and has a thickness not greater than about half of the height of the main channel. The deposit may be formed directly on one of the front and rear panels. Alternatively, the deposit may be formed on a support member, e.g., metal tape.
In another embodiment the nonevaporable getter device is at least one pellet comprised of sintered powder of a nonevaporable getter material. The at least one pellet is preferably disposed in a seat formed in an inner surface of one or both of the front and rear panels.
The at least one nonevaporable getter device may be formed of a variety of nonevaporable getter materials. Suitable nonevaporable getter materials include but, are not limited to, titanium, zirconium, titanium alloys containing a transition metal or aluminum, zirconium alloys containing a transition metal or aluminum, a mixture of titanium and a titanium alloy containing a transition metal or aluminum, and a mixture of zirconium and a zirconium alloy containing a transition metal or aluminum. The nonevaporable getter material is preferably in powder form having a particle size smaller than about 0.15 mm. Depending on the technique used to form the nonevaporable getter device, it may be desirable to use nonevaporable getter material powder having a particle size smaller than about 128 xcexcm or even smaller than about 60 xcexcm.
Preferred nonevaporable getter materials include an alloy containing 70 wt % of Zr, 24.6 wt % of V, and 5.4 wt % of Fe, an alloy containing 84 wt % of Zr and 16 wt % of Al, an alloy containing 76.5 wt % of Zr and 23.5 wt % of Fe, an alloy containing 76 wt % of Zr and 24 wt % of Ni, and a mixture containing 60 wt % of the alloy containing 70 wt % of Zr, 24.6 wt % of V, and 5.4 wt % of Fe and 40 wt % of zirconium.
In another aspect of the invention, a plasma flat panel display is provided. The plasma flat panel display includes a front panel, a rear panel, and a plurality of walls disposed between and in a center region of the front and rear panels. The walls define a plurality of secondary channels in the center region of the front and rear panels and a main channel along an internal periphery of the front and rear panels. A nonevaporable getter device is disposed within the main channel.
In one embodiment the front and rear panels are sealingly joined together at peripheral edges thereof, and an inner surface of each of the front and rear panels carries a series of electrodes. The series of electrodes carried by the inner surface of the front panel is orthogonal to the series of electrodes carried by the inner surface of the rear panel. In this embodiment the center region of the front panel defines a display area, and the walls extend substantially throughout the center region, with the main channel being adjacent to a periphery of the center region. The secondary channels have openings at each end thereof, and the nonevaporable getter device is preferably disposed within an area of the main channel that faces the openings at one end of the secondary channels.
If desired, first and second nonevaporable getter devices may be disposed within the main channel. The first nonevaporable getter device is preferably located within an area of the main channel that faces the openings at one end of the secondary channels and the second nonevaporable getter device is preferably located within an area of the main channel that faces the openings at the other end of the secondary channels.
As described above, the at least one nonevaporable getter device may be either a deposit comprised of powdered nonevaporable getter material or a pellet comprised of sintered powder of a nonevaporable getter material. When the nonevaporable getter device is in the form of a deposit, the deposit preferably continuously covers the area of the main channel that faces the openings at one end of the secondary channels and has a thickness not greater than about half of the height of the main channel. The deposit may be formed directly on one of the front and rear panels or on a support member, e.g., metal tape. When the nonevaporable getter device is in the form of a pellet, the pellet is preferably disposed in a seat formed in an inner surface of one or both of the front and rear panels. Whether in the form of a deposit or a pellet, the nonevaporable getter device may be formed from the nonevaporable getter materials described above.
The getter system of the present invention provides significant advantages during both the manufacturing and the service life of a plasma flat panel display. During manufacturing, the getter system acts as an additional pump in the main channel of the plasma flat panel display. This prevents the problems associated with gas discharge through the main channel and enables lower residual pressures to be obtained within the inner space of the plasma flat panel display, thereby reducing the pumping time required to evacuate the inner space. Over the course of the service life of the plasma flat panel display, the getter system of the invention provides constant pumping action that continuously removes the gaseous impurities generated by degassing of the materials from which the components of the display are formed. This ensures proper operation of the display by keeping the composition of the rare gas mixture within the inner space constant.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.